In the field of electro-acoustic products, the microphone is a sensor that converts acoustic energy into electrical energy. A capacitive micro-electro-mechanical system (MEMS) microphone generally includes a vibration membrane, a fixed plate (back plate), and a cavity between the vibration membrane and the fixed plate. A capacitive MEMS microphone enables detection of a capacitive value change due to the displacement of the vibration membrane caused by a change in the acoustic pressure, and the detected capacitive value change is then converted to an electrical signal for processing.
In some MEMS microphones, the cavity is formed using a wet etch (e.g., a buffered oxide etch) process to remove SiO2, so that the vibration membrane can move in the cavity.
FIG. 1 is a cross-sectional view illustrating an intermediate stage of a microphone according to a conventional manufacturing process. As shown in FIG. 1, an etch process is performed by introducing an etching solution via through-holes of a cover layer 3 into a structure below the cover layer to remove a portion of the structure to form a cavity surrounded by a substrate 1, a vibration membrane 2 and cover layer 3. In this process, vibration membrane 2 may be deformed due to the impact of the etching solution. When vibration membrane 2 is deformed to a certain extent, vibration membrane 2 may be broken, as shown in FIG. 2.
To overcome this problem, a technique of reducing the critical dimension (CD) of the substrate has been proposed. In the proposed technique, when a dry etch process is performed on substrate 1 to form an opening 4, the area of a corresponding mask is reduced so that the peripheral edge of opening 4 can provide support to vibration membrane 2 to prevent breakage during an excessive deformation of the vibration membrane. FIG. 3 is a plan view of a reduction in the size of a mask according to the prior art. Referring to FIG. 3, the mask shown in the left-hand side is a conventional mask, and the mask shown in the right-side is the conventional mask of the left-side that is reduced in size.
However, in this case, when substrate 1 is in contact with vibration membrane 2, the contact area is relatively large and may adversely affects the audio signal, resulting in deterioration of the microphone performance.